Unity Post-processing PostProcessEffectRenderer shows in Editor but not in build

Question

After adding an implementation of a PostProcessEffectRenderer to the Unity post-processing stack the effect works perfectly in the Unity Editor, but does not show in the built game.

Changes to build quality have no effect, effect does not show using maximum quality settings, building for Windows x86_64.

Grayscale.cs

using System;
using UnityEngine;
using UnityEngine.Rendering.PostProcessing;

[Serializable]
[PostProcess(typeof(GrayscaleRenderer), PostProcessEvent.AfterStack, "Custom/Grayscale")]
public sealed class Grayscale : PostProcessEffectSettings
{
    [Range(0f, 1f), Tooltip("Grayscale effect intensity.")]
    public FloatParameter blend = new FloatParameter { value = 0.5f };
}

public sealed class GrayscaleRenderer : PostProcessEffectRenderer<Grayscale>
{
    public override void Render(PostProcessRenderContext context)
    {
        var sheet = context.propertySheets.Get(Shader.Find("Hidden/Custom/Grayscale"));
        sheet.properties.SetFloat("_Blend", settings.blend);
        context.command.BlitFullscreenTriangle(context.source, context.destination, sheet, 0);
    }
}

Grayscale.shader

Shader "Hidden/Custom/Grayscale"
{
    HLSLINCLUDE

        #include "Packages/com.unity.postprocessing/PostProcessing/Shaders/StdLib.hlsl"

        TEXTURE2D_SAMPLER2D(_MainTex, sampler_MainTex);
        float _Blend;

        float4 Frag(VaryingsDefault i) : SV_Target
        {
            float4 color = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, i.texcoord);
            float luminance = dot(color.rgb, float3(0.2126729, 0.7151522, 0.0721750));
            color.rgb = lerp(color.rgb, luminance.xxx, _Blend.xxx);
            return color;
        }

    ENDHLSL

    SubShader
    {
        Cull Off ZWrite Off ZTest Always

        Pass
        {
            HLSLPROGRAM

                #pragma vertex VertDefault
                #pragma fragment Frag

            ENDHLSL
        }
    }
}

Answer 1

After much trial and error I realised that this was caused by Unity excluding the hidden shader as it lacked a reference to anything in the game at build time. On build Unity will only include shaders either attached to a material in use in a scene or those added in project settings in the 'Always Included Shaders' array.

I tried both and it solved my problem, it has been suggested that creating a dummy object within your game referencing the hidden shader will work better as it leaves Unity to decide if it's needed in a scene or not. Either way this fixed it for me.